For semiconductor manufacturing facilities, many gas supply systems have been conventionally used in which various types of liquefied gases for semiconductor manufacturing are received into their tanks and are gasified by their vaporizers, and then are supplied to process chambers. For example, FIG. 12 shows an example of a basic configuration of a gas supply apparatus composed of a vaporizer Va and a liquid type thermal mass flow rate control device LMFC. The gas supply apparatus is configured so that a liquefied gas LG, received in a liquefied gas receiving tank T, is fed to the vaporizer Va by use of the pressure of a gas Gp for pressurizing or by the use of a pump for feeding liquid (not shown), while controlling its flow rate by the liquid type thermal mass flow rate control device LMFC, in order to supply a vaporized gas G at a predetermined flow rate to a process chamber CH. In addition, reference character H is a heating region.
Meanwhile, because the liquid type thermal mass flow rate control device LMFC is used for the gas supply apparatus of FIG. 12, there is the problem that an error in a vaporized gas flow rate becomes inevitably large even when an error in flow rate control in a liquid state is small. This makes it difficult to accurately control gas flow rate.
Therefore, as shown in FIG. 13, a gas supply apparatus of a type in which a high-temperature type thermal mass flow rate control device HMFC is connected to the downstream side of the vaporizer Va has been developed to make an attempt to perform highly accurate mass flow rate control of a vaporized gas G. However, because the high-temperature type thermal mass flow rate control device HMFC has the characteristic that controlling flow rate is greatly changed according to fluctuation of a primary side flow rate and pressure, it is necessary to maintain a secondary side flow rate and pressure of the vaporizer Va at predetermined setting values by highly accurately performing temperature control on the side of the vaporizer Va in order to perform highly accurate flow rate control for the gas flow rate. Furthermore, it is necessary to set a temperature of its sensor portion to be higher than a temperature of its main line in the high-temperature type thermal mass flow rate control device HMFC, which may easily bring about decomposition and deposition of the liquid source (material).
On the other hand, in order to highly accurately maintain the secondary side of the vaporizer Va at a predetermined flow rate and pressure, it is necessary to highly accurately perform temperature control of the vaporizer Va as described above and, as a result, it is necessary to increase a heating volume and enlarge a heating region. Therefore, not only is the gas supply apparatus itself increased in size by necessity, but also various inconveniences are brought about in terms of energy saving, operating cost, and the like.
[Patent Document 1] Japanese Published Unexamined Patent Application No. H11-278987
[Patent Document 2] Japanese Published Unexamined Patent Application No. 2003-142473
[Patent Document 3] Japanese Published Unexamined Patent Application No. 2004-143591
[Patent Document 4] Japanese Published Unexamined Patent Application No. 2007-036265